1. Field of the Invention
The present invention relates to a legged mobile robot having at least a plurality of movable legs and to an actuator device applicable to a joint shaft of the legged mobile robot, and in particular relates to a legged mobile robot having sensors, such as an acceleration sensor, an angular velocity sensor, and a torque sensor, for detecting actuator driving situations and sensors, such as a touch sensor and a pressure sensitive sensor, for detecting contact and collision with surroundings and to the actuator device applicable to the joint shaft of the legged mobile robot.
In more detail, the present invention relates to a legged mobile robot having sensors, such as a position sensor, an acceleration sensor, an angular velocity sensor, and a torque sensor, housed every joint actuator for detecting actuator driving situations, and sensors arranged outside the actuator for detecting contact and collision with surroundings and to the actuator device applicable to the joint shaft of the legged mobile robot, and in particular it relates to a legged mobile robot suitably communicating signals for drive-controlling each joint actuator, output signals from the sensors housed in the actuator, and output signals from the sensors arranged outside the actuator with a higher-order control system and to the actuator device applicable to the joint shaft of the legged mobile robot.
2. Description of the Related Art
A “robot” means a mechanical apparatus simulating a human movement using electrical and magnetic functions. The etymology of the robot is a Slavic “ROBOTA (slave machine)”. In Japan, the robot has been widely used from the late 1960s, and many of the robots at that time are industrial robots, such as manipulators and carrier robots, for automating and unmanning manufacturing operations in factories.
By a floor-type robot, such as an armed robot, component assembling and selecting are performed only within a fixed and local operating space by being transplanted at a specific position. Whereas, the operating space of a mobile robot is non-restrictive, so that the mobile robot can carry out pre-determined or arbitrary operation for a human, and provides various wide services instead of a living matter, such as a human and a dog, by freely moving along a route or a non-route. Among them, a legged mobile robot is excellent in that it can achieve flexible walking operation, such as moving up and down a step or a ladder and hurdling obstacles, regardless of a non-finished ground, although the legged mobile robot is unstable and difficult to be controlled in attitude and walking in comparison with a crawler-mounted robot and a tire-mounted robot.
Recently, the research and development have been progressed about legged mobile robots such as a pet-type robot simulating the physical mechanism and operation of four-footed animals, such as dogs and cats, and a human-shaped or human-type robot called as a humanoid robot designed by simulating the physical mechanism and operation of two-footed animals, such as a human, waling in erected posture as a model, so that the practical application thereof is expected.
A legged mobile robot reproducing a human living body mechanism is called as a human-shaped or a human-type robot (humanoid robot). The human-type robot can support human activities in various situations of every day life under living conditions.
Almost the entire human operational space and living space are formed corresponding to the physical mechanism or the behavior pattern of two-footed walking humans, so that there are a number of obstacles, against which a present mechanical system must move using driving devices such as wheels as a moving unit. Therefore, in order to act for various human operations and to deeply infiltrate into a human living space for a mechanical system, i.e., a robot, it is preferable that the movable range of the robot be substantially the same as that of a human. This is also a reason for that the practical application of legged mobile robots is expected.
Such a legged mobile robot generally has a number of degrees of joint freedom so as to achieve joint operation with actuator motors. Also, by servo controlling with a rotational position and a rotational amount derived of each motor, a desired operational pattern is reproduced while a posture is controlled.
A servomotor making up the joint freedom must be designed and manufactured in a small size and high performance. Therefore, there has already been a small-sized and gear direct-attachment type AC servomotor having a servo-control system built therein and applicable to a joint actuator of the legged mobile robot (see Japanese Unexamined Patent Application Publication No. 2000-299970, for example).
However, in a conventional unitized actuator, harnesses for a power supply and control signals are exposed from an actuator body. Also, to an output shaft connected to a rotor of an actuator motor, only a mechanism to be connected to a structural member is added.
Therefore, for a user (or a designer), in order to construct a multispindle robot using such an actuator unit, it is necessary to design a harness to be routed through various movable units.
Most proposals about the attitude stable control or the prevention from overturning during walking are using a ZMP (zero moment point) as the norm for determining the degree of stability (see “LEGGED LOCOMOTION ROBOTS” by Miomir Vukobratovic, and “HOKOUROBOTTO TO JINKOU NO ASHI (WALING ROBOT AND ARTIFICIAL LEGS)” by Ichirou KATO et al., and published from THE NIKKAN KOGYO SHIMBUN, LTD., for example). By two-footed walking pattern generated based on the ZMP norm, there are advantages that a landing site of a sole can be set in advance, and that kinematic restriction conditions of the front leg may be easily considered. Also, the ZMP as the norm for determining the stability does not mean a force but a trajectory as the desired value of the motion control, so that technically achieving expectation is increased.
When strictly controlling the movement of a legged robot according to a ZMP equation, an acceleration in a world coordinate limited to a local coordinate used in the control, a position (posture) and an acceleration at each region of the robot in a local coordinate system, a ZMP position, an external force, an external force moment are measured so as to introduce the measured results in the ZMP equation. Thereby, the position and the acceleration at each region can be controlled while an unknown external force moment and an unknown external force are identified so as to strictly control the movement.
For example, one clinometer (or one acceleration meter) and one gyroscope arranged at each of shafts (pitch, roll, and yaw) (X, Y, and Z) so as to have a six-shaft force arrangement are arranged at each region having an external force applied or assumed to have an external force applied and at a position separated to that having the external force applied in practice for controlling the movement with the minimum number of sensors. However, in the movement control system with such sensor arrangement, it is difficult to directly measure and control the positions and accelerations at the entire regions in addition to the accelerations limited to the local coordinate used in the control. This cannot assure the movement control of a robot aimed at the stable walking on a ground such as gravel and a thick carpet, which are liable to move if a force or a torque is applied, and a tile in a residence liable to produce slippage with a small frictional coefficient when moving in parallel; and at gross movement including jumping by adding flexibility to the robot itself.
Whereas there is a proposal that an acceleration sensor, an angular velocity sensor, and a velocity sensor for directly measuring a local coordinate used for the control and its coordinate are arranged every control point and an acceleration sensor and a posture sensor are further arranged every vector position used in a computation model (see Japanese Patent Application No. 2002-297207, for example). Thereby, a control parameter value necessary for introducing the ZMP equation (or an equation of motion) can be directly measured. As a result, the strict motion control can be achieved with good responsiveness and without the assumption that the robot is rigid and does not deflect by an applied external force.
However, in order to make assurance of the posture-stability control of the robot, acceleration sensors, angular velocity sensors, and velocity sensors need to be compactly arranged in various regions of the robot for transmitting sensor outputs from locals to the central control unit. In such a case, it is necessary to design harness to be routed through various movable units.
In such a legged mobile robot with a high degree of freedom having mechanical movable units so as to exchange information with a human for entertainment, there are various situations deviated from the operation condition assured by the control system of the robot. For example, in a case where a human exchanges information by touching a robot, different from a toy robot, it is difficult for a user to expect the robot operation, so that there is a problem of a danger that a finger, etc., is pinched by the movable unit. There is also a problem that a user is difficult to enjoy the information exchange by awful feeling due to the danger.
Accordingly, there is a system proposal that torque sensors are arranged at joint regions, each having a wide movable range and being in danger of pinching or catching a user, so as to automatically detect the pinching or the catching based on the sensor output (see Japanese Unexamined Patent Application Publication No. 2002-342963, for example). In this case, upon detecting pinching a user' finger, etc., at a predetermined region, the legged mobile robot executes the operation for avoiding this. Thereby, the robot aimed at to exchange information with a human for entertainment can be prevented from the danger in that a finger or the like is pinched by the movement of the movable unit. In this case, there are advantages that a protective robot is provided and information exchange can be enjoyed with the robot at ease without awful feeling.
However, in order to further make assurance of avoiding the danger during movable time of the robot, torque sensors and temperature sensors need to be compactly arranged in various joint regions of the robot. With regard to the pinching and the interference with another object in detail, only the sensor information inside the actuator, such as torque detection, is insufficient so that sensor information from a sensor, such as a pressure-sensitive sensor, disposed outside the casing is required.
In such a case, in order to transmit sensor outputs from locals to the central control unit, it is necessary to design harness to be routed through various movable units.
When signal lines for transmitting sensor signals of the above-mentioned sensors are viewed in addition to signal lines for drive controlling actuators, it is impossible to design harness to be routed.